If they got better is a matter of opinion. They lost all of their original members and were no longer "underoath" but kept the name. Until recently, because fans and most likely the members themselves noticed how dumb it was to try to keep going under that name.
Really? You see he dudes that played on Act of Depression as a bigger part of Underoath than the people that have been playing in it since 2004? The guys no one can even name that played on a demo or two are more deserving of the title? I honestly don't even see Underoath as "being Underoath" until TOCS, when they finally solidified a sound. Then they moved forward with that sound and losing Aaron was the natural progression of that. I totally think it made sense for them to keep the name. Its not like the guys that were in the band for six months back in 2001 gave a shit about them using it.